Ink jet printers employ print heads that reciprocate over a media sheet and expel droplets onto the sheet to generate a printed image or pattern. In some ink jet printers, an ink supply connected to the print head reciprocates along with the print head. To reduce operating costs, some ink jet printers use ink supplies that are separately replaceable, so that the print head is not discarded when an ink supply is depleted. The connection between such a print head and replaceable ink supply faces some difficulties.
First, it is important to make a disconnectable fluid connection between the ink supply and the print head that does not leak, either when the components are connected to each other, or when separated for ink supply replacement. A connection should be repeatable without degradation, readily aligned or tolerant of misalignment, compact, reliable, and inexpensive.
A second concern with removable ink supplies involves the introduction of gas into the print head. Gas may be introduced by way of ink containing dissolved gas that outgasses in a print head chamber, or due to air entrapped upon connection of an ink supply. Gas bubbles can block the flow of ink, and can lead to ink degradation, drying, or crusting.
Existing supply/print head interface systems may employ a foam-filled ink supply, and a mesh covered conduit on the print head that presses against the foam. While effective, foam systems reduce the volumetric efficiency of the supply cartridge, are subject to ink crusting at the openings when the components are separate, and are vulnerable to leakage without additional sealing.
Other contemplated systems for a supply/print head interface involve the use of a needle and septum, with a hollow needle on the print head, and a septum on the ink supply sealing the opening. This requires additional sealing to prevent the needle from drying out when the supply is removed, and the system tends to be more bulky and complex than would be most desirable. The septums may be damaged or deformed, with a particular concern involving an inexperienced user repeatedly reinstalling a single ink supply due to a lack of confidence about whether the installation was correct. Further, such systems are intolerant of moderate misalignments, and rely on elastomeric components that can be troublesome to procure.
The present invention overcomes the limitations of the prior art by providing an ink jet printing system with a pen body having a first chamber and a second chamber. A print head on the pen body is connected to the second chamber, and an ink-transmissive barrier separates the second chamber from the first chamber. A pump is connected to the pen body in communication with the first chamber, and operates to generate a positive pressure in the first chamber to motivate ink from the first chamber, through the barrier, and into the second chamber. An ink supply cartridge may be provided that removably connects to the pen body, and which has openings in registration with corresponding openings in the pen body into the first and second chambers, respectively. A sliding shutter or other valve may be provided on each of the pen body and the cartridge to close the openings when the cartridge is removed from the pen body. An actuator portion of the cartridge may operate to engage the pump upon installation of the cartridge, and to displace any gas bubble from the second chamber to the supply cartridge; upon disengagement of the cartridge, the actuator may release the pump, drawing ink from the cartridge into the first chamber.